Apparatus for rectifying or for converting alternating or direct current



q 1940-. FQKESSELRING 2, ,4

APPARATUS FOR RECTIFYING .OR FOR CONVERTING ALTERNATING 0R DIRECT CURRENT Filed Jan. 15, 1am 3 Sheets-Sheet 1 RELAY/U J'HOWN /N CONT/90L DEV/CE Afff/OWIV WI /63 1M Wu, We

Sept. 24, 1 40- F. KESSELRING 2,215,471

APPARATUS FOR RECTIFYING OR FOR CONVERTING ALTERNATING 0R DIRECT CURRENT I Filed Jan. 13, 1937 3 She ets-Sheet 2 vii.

p 24, 1940- F. KESSELRING 2,215,471

APPARATUS FOR RECTIFYING OR FOR CONVERTING ALTERNATING OR DIRECT CURRENT Filed Jan. 13, 1937 3 Sheets-Sheet 3 mm m I20 Patented Sept. 24,}940

I mmrns roa ascrrrrnve on ron GON- vaa'rmo ALTEBNATING on manor coa- BENT Fritz Kesselring, Berlin-Frohnau, Germany, assignor to Sicmens-Schuckertwerke Aktlengesellschai Berlln- Siemensstadt, Germany, a

corpora on of Germany Application January 13,1937, Serial No. 120,429 I In Germany January 13, 1936 12mins- My invention relates to apparatus for rectifying alternating current or for converting direct current into alternating current or for converting altenating current of one irequency into alternating current of .a diiierent irequency, and more electric converting device simple in construction and reliable in operation. A

Another object of my invention consists -in adapting the commutatin'g operation of a mechanically actuated converter to the load fluctuations of the converter.

Other objects '0! the invention will become 20 apparent from the following description.

The invention is .based on,the idea that in a co verter of the above-mentioned type, the curwk interrupted in the current phase to be disco 'ected, only at the moment when the commutation current of this phase passes its zero value. In this case, the flow of current in the reverse direction can be ayoided with certainty only if the opening gap, formed at the time when 36 the current passes through its zero value, is able to withstand a'high voltage without being punctured. In this respect it is possible to determine for each. circuit breaking device certaincontact I distances which, if attained during the progressing opening movement of the contacts, prevent with certainty areignition. f

A difl lculty arises from the fact that upon load fluctuations, the time necessary for the commutation, i. e. the interval between the closing of the commutation circuit and the passage of the current through the zero value, increases with increasing load.. The known relatively sluggish control devices used in connection "with rotary rectiilers, which permitshiitlng the instant oi the contact separation in accordance with load variation's,are only suitable for relatively slow fluctuatiens oi load. For the purposesoi the invention, i. e. to attain minimum gas discharges for all loads likely tooccur in practice, this control must 5 be able to follow load variations'instantaneously even ii they occur within a halt cycle of the alternating current. To this end, according to a feature 01 my invention, the drivins devices and the control devices are so designed as to have so little to sluggishness that they control the contact separation in accordance with a definite instantaneous value or upon the rate of change of the descending curve portion of the current to be interrupted. These driving and control devices operate, therefore, with a speed adapted to the rapid varia- 5 tions of the commutation current and to the short period of commutation. i

The magnitude and the rate of change of the commutation current; which determine the duration of the commutation period, are measurable 10 at the moment when the circuit is closed. -It is consequently possible to provide the necessary control of the contact movement, provided the control devices operate in a correspondingly rapid manner. If a little more time is desired for the control of the contact movement, the control device may be influenced only in dependence upon the magnitude of the load current flowing before the commutation period.

However, when the control of the contact move-- ment'is to be efiected in dependence upon the rate of change of the decreasing current flowing in the decaying phase during the commutation. period, a self-saturating reactor may be used, and the voltage induced in this reactor while it passes from the saturated to the desaturated state may be employed to operate a relay which governs of the adjusting devices must be made as small as possible, and the force accelerating the mass as great as possible. Theadjusting path should be made as short as possible, which may be accomplished by arranging the interrupting devices in a gaseous medium of high disruptive strength and under high pressure. Extinguishing devices may be used to clear the opening gap rapidly of 4 the discharge carriers. The amplification of the control impulse for the force required to break the contacts must also be efiected as far as possible without sluggishness, foninstance by amplifier tubes or similar quick-acting devices. I Further features of the invention will be apparent from the following description taken in .connection with the accompanyingdrawings in which some embodimentssoi my invention are illustrated. Inthe drawings:

Fig. 1 shows in diagrammatic form a polyphase rectifier according to my invention and the devices cooperating therewith,

Fig. 2 is a graph showing the voltages and the currents of the same rectifier,

Fig. 3 illustrates certain details of the arrang ment of Fig. 1,

Fig. 4 shows, partly in section, another form of another electric converting device according to my invention,

Fig. 5 is a vertical sectional view taken on the line IV IV of Fig. 4,

Fig. 6 is an elevational view of the electric converting apparatus shown in Fig. 4 with the casing partly broken away, and

Fig. 7 is a wiring diagram of the electric converting devices shown in Figs. 4 to 6 and of the apparatus cooperating therewith.

Referring at first to Fig. l, I denotes a transformer connected to the three-phase supply circuit U, V, W, The currents of the three secondary phases a, v, w flow through the interrupting devices 2, 3, 4 which may be designed in the form of known high-speed switches. These interrupting devices are so controlled that a rectified current feeding the current consuming device 5 may be taken from the secondary winding u, v, w of the transformer I. Springs I5 have a tendency to hold the interrupting devices 2, 3, 4 in the closed position. The openingof the interrupting devices is brought about by electromagnetic couplings 6 and a high-speed revolving body of relatively great mass formed of a steel belt I, which ,is passing over two pulleys 3, 9 and driven by any suitable motor ID. The steel belt has polished surfaces and runs through a narrow gap between the pole pieces of the magnets, the clearance between both sides of the belt and the pole surfaces amounting only to a few hundredths of a millimeter. The purpose of this drive is to give the contacts 2, 3, 4 an acceleration as great as possible in the opening direction.

The control of the electromagnetic couplings 6 is effected by relays II to which control impulses for opening the switch contacts are supplied from reactor coils I2 connected in the respective phase leads from the transformer I to the contacts. Impulses for closing the switch contacts are supplied by means of a control device I3 actuated synchronously with the alternating current to be recified. The magnet windings I4 of the couplings 6 have direct current batteries IB- are provided for the moving switch contacts. As

shown in detail in Figure 3, each relay II has a magnet core I I. with a movable armature carrying a contact 20 and provided with a spring 2I which normally holds the contact open. The core II carries an exciting winding I2, which is connected across the reactor I2 (Fig. 1), a holding win'ding I6 (Fig. 3) for the relay, this hold ing winding being connected to the battery I6 in series with the contact 20 and the coil I4 of the magnet coupling (Fig. 1), and finally, a further winding I3 connected with the control device I3. As shown in Fig. 1, there are three relays II, one for each phase, but a single control device I3 arranged to cause energization of the coils I3 of three relays in turn. The relay I3 has a rotating contact 23, which is driven by a synchronous motor 22 connectedto the supply mains UVW. The phase position of this motor may be accurately adjusted by a phase-shifter (not shown) or by rotating its stator winding relatively to the phase position of the feeding voltage. The rotating contact 23 of the relay I3 cooperates with stationary contacts I3u, I32), I310, which are spaced at 120 intervals around the circle swept over by the contact. One side of each of the windings I3 is connected to the rotating contact 23 while the other sides of these three windings are respectively connected to the three phases of the supply mains and to the three contacts I3u, I30, and I3w of the device I3. Thus .as the contact 23 rotates, an impulse is supplied to the coil I3 of each relay II in turn. The reactors I2 are provided with iron cores II which are so proportioned that they are highly saturated during the main portion of the period of the flow of current, i. e., in the interval between two points at which the current passes the zero value and desaturated below the mean value of the current, particularly at very low current values, for instance, of ,4 or of the amplitude value, occurring in the neighborhood of the point at which the current passes the zero value. This desaturation has the effect to increase the resistance of the reactor at low intensities of the current to be interrupted, which increased resistance tends to further suppress the intensity value of the current. The result is a flattening distortion of the current curve in the vicinity of the zero passages of the curve. In other words, due to the periodical increase of the resistance of the reactors, intervals are periodically established during which the current intensity remains at a very low value. Therefore the interruption of the current need no longer take place at the exact moment of the zero passage but may be effected during an extended weak current interval. The reactors thus make it possible to control high operating current intensities of hundreds and thousands of amperes, whereas the current intensity at the time when the interruption is effected by opening the contacts, is of an order of magnitude of only one ampere. Consequently the sparking at the contacts is considerably suppressed and the consumption of the contact material is reduced to such an extent as to ensure operativeness for a remarkably long time of operation. Reactors of the type here referred to, are also described in the copending application, Koppelman, Serial No. 114,965, filed December 9, 1936. In the following, such reactors are designated as switching reactors.

The magnet core I! of the switching reactors (Fig. 1) consists preferably of high-grade steel, such as Permalloy or Hyperm, the magnetization curve of which presents a high initial permeability and a sharp saturation bend. Separate control windings 20 on the cores I! serve to bias the cores with direct or alternating current from a power source 2I through a rheostat 22. These control means allow adjusting the conditions at which desaturation of the reactor occurs.

In order to explain the operation of the abovedescribed converter arrangement, the commutation phenomena occuring in mechanically operating rectifiers of the type here concerned, will at first be described in a general way with reference to the diagram shown in Fig. 2. The time t is plotted as abscissa, while the values of the voltage u and the currents J and i are plotted as ordinate. At A the phase voltages in and uz are equal. At this moment, two contacts of the rectifier are closed so that the two sequential phases carrying the voltages ur and uz are shortcircuited. The closure of the contacts may be effected, as the case may be, before or after 7 reaching the voltage equality in order to control the current in a known manner. Let iibe the current flowing in the first phase commutation. This current decreases in the period In to the zero value. In the same period In the current of the second phase increases from zero to the full value la. The separation of the contacts in the decaying first phase takes place at the instant B which is m seconds before the zero passage of the current. The time 1n isso chosen that the opening contacts of the decaying phase reach a break distance which ,is sufllciently great to eil'ect quenching of the arc and, to prevent with certainty a-flow of current in the reverse direction.

If new the load increases from the value 1 to the value J, then the current J1 of the phase to I be disconnected decays to zero in the period its,

curve.

how the operation-of the above-described at rangement according to the present invention diifersfrom that of the known rectiflers.

By the contact control according to the invention the moment of the contact separation is shifted in accordance with 'load variations; i. e. when the current increases from ii to 'Ji, the contact opening is shifted from the instant B to the instant G. This retardation is such that the breaking of the contacts takes place, as previously m seconds before the current J1 oi the phase to be disconnected passes through the zero value, and, therefore, the path produced is not greater than for the interruption. By the switching reactor l 2 the curve of the commutation current is distorted compared to the above-described The decaying portion of the commutation J1, for instance, no longer corresponds to the full-line curve in Fig. 2, but follows the dot-anddash portion J. In other words, due to the desaturation of the core II of the reactor l2 and the "rapid increase of the resistance of the reactor, the current curve is flattened and the current reaches a. very low value some time before it passes through the zero value. A similar weak current interval occurs at smaller loads, as the current in the decaying phase no longer follows the descending branch of the broken line 11 but is distorted as indicated by the dot-and-dash;

line i. The operating periods otthe relays II and i3 of the magnetic couplings. i, of the contacts 2, 3, 4, of the driving devices I, 8, v9 and the magnetic bias of the switching reactors are so tuned that the points B and C (Fig. 2) at which the contacts are broken lie as far as possible at the beginning of the weak current interval and that at the moment at which the current passes the zero value the contact distance which 1 is capable of preventing with certainty. the 110w of current in the reverse direction is attained, but not appreciab y surpassed, i. e., for instance, the actual distance should not be greater than double the length of the mentioned minimum distance. Inthis case the circuit will be interrupted practically without sparking at all possible loads in operation, since both the effective range of the switching reactor and the contact break are automatically adapted to-the varying period of commutation.

-The circuit of the battery i6 (Fig. 1) is thus phase ii the production of the switching impulse 'the switching device'2 is very rapidly opened as direct-current load is fed from the phase u. The magnetic coupling of the switch 2'is deenergized so that the switch is held closed by its spring i5, 5 whereaslthe magnetsof the switches 3 and 4 are energized. The pole pieces of the magnets'of switches I and *4, owing to a small deformation of the magnets, contact with the steel belt'l passing therebetween and are, consequently, displaced by the belt inthe direction of the arrows It. The switches 3 and l are, therefore, held in the open position against the action of the springs. u

A moment later,.i. e., as soon as the increasing phase voltage (voltage u: in Fig. 2) of the incipient phasew is equal to the decreasing voltage (in in Fig.2) of the decaying phase 11. (that is, at the instant A in Fig. 2), the rotating arm 23 of the device It (Fig. 3) engages the contact law,

and the winding I3 of the relay ll of phase 10 20' is energized. This energization counteracts the effect of the holding coil l6 so that now the armature 20 is released and is moved by its spring 2i too the position shown in full lines in Fig. 3.

broken in the phase w and the contact 4, consec quently, is closed by its spring l5. This establishes a short circuit of the phases u and w, through the interrupters 2 and l.

The alteration of current during the'commutation sets up across the reactor coil I2 oi phase u (and also phase walthough this is not material) a voltage which drives a current through the exciting coil H of relay Ii of phase u. If the talling commutation current drops below the value at which the core I! of the reactor i2 is saturated, a sudden increase in the rate 01' change of the current occurs, as a result of which the voltage across the reactor coil l2 increases, the excitation of the coil i2 being co sequently also increased. This causes relay il attract its arma ture 20 against the s aring 2| and to closethe circuit of the battery. is through the holding coil It, so that the armature remains attracted when the voltage produced in the coil l2 and conserate at which this short-circuit current disappears, controls through the reactor 12 of the for opening the switch contact 2. Due to the kinetic energy of the moving mass 1, ,which must be made high in comparison with the moving mass of the switch device, the moving contact of soon as the magnetic coupling is completed by the excitation ofthe coil M. The acceleration of this opening motion is so great that the contacts are separated the necessary distance within a time of about one thousandth of a second. This vided with extinguishing device: of known type.

The interrupting devices may be designed in the form of other high-speed switches, the contacts of which are opened under the action of powerful springs as soon as a holding magnet is demagnetized. Also with some known constructions of this type, it is possible to attain the extreme high break speeds which are essential for carrying out the invention.

If the switching reactors .I2, I1 are rated for a greater inductance than as above described with reference to Fig. 2, the weak current pause is thereby lengthened. In this manner, a certain space time interval is attained. Therefore it is no longer necessary that the contact distance capable of preventing with certainty a flow of current in the reverse direction be attained at just that moment at which the current passesthe zero value. This contact distance must, however, for all loads occurring in operation, be attained at the latest at that moment at which the instantaneous value of the current surpasses again the value of saturation of the reactor. It is preferable to arrange the driving apparatus and the control apparatus for the contacts 2, 3, 4 in such a manner that they always commence to open at the beginning of the weak current interval. An electric converting device thus equipped will utilize the current-reducing effect of the selfsaturating switching reactor so as to improve the commutation for all loads occurring in operation, irrespective of the displacement of the points at which the current passes the zero value caused by the'load fluctuations in such a manner that the sparking is substantially suppressed.

If the switching reactor is to be employed only for bringing about a Weak current interval, a separate control reactor may be employed for controlling the contacts, the control reactor preferably being shunted across the main current path.

While the contact device shown in Fig. l is provided with reciprocatory contacts, Figs. 4 to 6 illustrate another electric converting device, the contact device of which is equipped with a revolving contact IOI and in which an additional switch motion, caused by the control devices, is imparted to the stationary counter-contacts I02, I03, I 04 and superimposed upon their continuous rotation.

Fig. '1 shows a wiring diagram of this electric converting device in connection with the supply transformer I and the necessary auxiliary devices.

The revolving contact IOI is, as shown in Figs. 4 to ,7, secured to the shaft I00. In the contact .IOI is arranged a passage I55 for extinguishing gas. The passage I55 ends on the one hand in an opening I54 and on the other hand in a bore I56 0f the shaft I00 leading to the outside atmospheriz. A counter-weight IOIa serves to compensate the revolving masses. The shaft I00 is mounted at one side in a metallic bushing I41 to which is connected a pole of the direct-current line with the terminal I46. The metallic bushing I41 is arranged with an insulating intermediate layer I48 in the casing MI. The shaft I00 is driven by the synchronous motor IIO whose end bearing shield IIOa, designed in the form of a flange, is so secured to the casing I4I as to form a gas-tight closure thereof. The casing MI is supported on feet I45. On the shaft I00 a disc I01 is loosely mounted. The latter has a flange I01a with internal gearing and is driven through an intermediate gear I08 by a pinion I09 firmly secured to the shaft, the gear I08 being mounted in the extension I48 of the end bearing shield IIOa. The disc I01 rotates in a direction opposite to that of the revolving contact IOI.

At the periphery of the circular path (shown in Fig. 5 as dash-and-dot circle) of the revolving contact IN the stationary counter-contacts I02, I03, I04 are angularly spaced They are held by contact supports I40 which are secured with insulating arms I30 to three rings I32, I33, I34 loosely mounted on the shaft. The arms I30 are provided with extensions I3I and are held in the position of rest firmly in contact with the stops I36 by tension springs I31 secured to eyes I38. Further stops I35 are arranged in spaced relation to the stops I38 in the direction of rotation of the disc I01.

Magnets I06 provided with energizing windings I I4 are secured to the contact supports I40. The pole pieces of these magnets are placed over the flange I01b of the disc I01, the flange I01b consisting, for instance, of ferromagn tic material. The exciting windings II4 are connected to the relays III, which in turn are connected to the ends of the switching reactors H2 and the control device II3 through conductors which transmit the control impulses. The switching reactors II2 are connected to the stationary contacts I02, I03, I04 through flexible conductors. The other end of the switching reactors is connected through the terminals I24 to the sec ondary windings u, v, w of the supply transformer I whose primary winding is connected to the supply circuit U, V, W. Also the intermediate relay H3 is connected to the terminals I24. The devices III and H3 correspond to the devices II and I3 shown in Fig. 1. They are secured to the flange I I0a. Auxiliary terminals I49 for the con nection of direct-current sources II6 are arranged on the outer side of the flange I I Do. The auxiliary terminals I43 are connected with the relays III by insulated conductors passing through the flange IIOa. Further auxiliary terminals I39 are arranged on the casing I4I. Insulated conductors lead from these terminals to the exciting windings I20 which serve to bias the iron cores I I1 of the switching reactors I I2. The auxiliary terminals I39 are connected in pairs with one another in such a manner that the biasing windings I20 are connected in series. From the outermost terminals extend conductors through a variable resistance I22 to a power source I2I which supplies the magnetization current,

On the flange IIOa is further arranged a gas connecting nipple I53 to which is connected through a pressure-reducing valve I52 and a conduit I5I a steel flask I50 containing extinguishing gas. The flask I50 is easily interchangeable.

The synchronous driving motor IIO is connected to the secondary windings u, v, w of the supply transformer I through a phase advancer II9. The second pole of the direct-current conductor extends from the neutral point of these windings to the current consuming device I05 and then to the terminal I46 through a reactance coil I60.

In operation the contact IOI revolves in the direction in which it passes in the sequence indicated the stationary contacts I02, I03, I04. The disc I01 rotates in the opposite direction.

If, for instance, in the position shown the magnet secured to the contact I02 is energized by an impulse derived from the switching reactor I I2 connected in series with the contact I 02 and said terior of. the 'casing' Ill,

' the circuit of the converting device so as to be impulse after amplification is transmitted by the relay III belonging to the same phase, the contact I02 is magnetically coupled-to the revolving disc I01 and moved against theaction or the spring I31. In this manner, the contact break is effected sooner than if the contact I02 would remain in its position of rest. The contact break thus commences at the beginning of the weak current interval caused by the switching reactor and the contact distance necessary for preventing backfires'is attained at the latest at the end ,of the weak current interval.

The extinguishing gas, for instance air, flows from the flask I50 under high pressure through the conduit I5I and the valve I52 into the in- The valve I52 reduces the gas pressure to a lower value, for instance, to 5 atmospheres. The whole casing MI is, consequently, under a uniform inner superatmospheric pressure. The gas flows after having alternately extinguished the arcs at the contacts I02, I03, I04 through the opening I54 of the contact IOI, through the passage I55 of this contact, through the passage 156 of the shaft I to the outsideat-- mosphere. A collecting tank with a conduit may also be connected to the passage I56. The extinguishing gas collected in the tank may be purified,

filled under pressure in flasks and employed again for the extinction of arcs. j

While I have shown and described in detail two specific embodiments of my invention, it is to be understood that such showing and description is illustrative only, and for the purpose of making my invention more clear, and that the invention is not to be construed as limited to these details,

altenating current or alternating current of one frequency into alternating current of another frequency, comprising mechanical contact interrupters each having a movablecontact and a counter-contact, driving means for periodically actuating saidinterrupters, means for transmitting the movement from said driving means to said movable contacts, and quick acting means for causing the opening of said interrupters to take place after the current to be interrupted has reached a predetermined instantaneous value which is lower than a current injurious to said contacts, said quick acting means being electricurrent into cally'coupled with the circuit of said converting device so as to becontrolled in response to the current flow passing said device and being designed to react upon the current flow du' he descendent curve part of the period immed tely preceding the opening movement of the interrupter to be biased.

2. An arrangement for converting alternating irect current or direct current into alternating durrent or alternating current of one frequency "i'nto alternating current of another frequency, comprising mechanical contact interrupters each having a. movable contact and a counter-contact, a common driving mechanism for periodically operating said interrupters, means for coupling said driving mechanism with said interrupters, and quick acting means for controlling the operation of said coupling, said quick acting means being electrically connected with operated in response to the current flow passing the interrupter to be opened anrVbeing designed to effect the opening of said interrupter after the current has decreased below a predetermined ill-- stantaneous value which is lower than a current injurious to said contacts. e

quency, comprising mechanical contact interrupt-- ers each having a movable contact and a countercontact, a drive for said movablecontacts at the frequency of the current to be interrupted, and a quick acting current responsive device operatively connected with said counter-contacts and designed to impart an additional movement to said counter-contacts, whereby the moments at which the contacts are broken in the phase to be disconnected are shifted in response to the commutation current of the half cycle to be disconnected.

4. An arrangement having movable break contacts in each phase for converting alternating current into direct current or direct current into alternating current or alternating current of one frequency into alternating current of another frequency, comprising a drive for said contacts at the frequency of the current to be interrupted, an inductance in each phase connected in series with the contact of said phase, and a quick acting relay in' each phase connected with said inductance of said phase so as to be energized by the voltage which is produced in said inductance by the commutation current and proportional to the speed with which the commutation current varies, said relay being designed to influence the movement of the contact of the phase to be disconnected in such a manner that when the-current passes the zero value that length of the contact break is attained at which a flow of current in the reverse direction is prevented with certainty.

5.- A multiphase current coverting device for converting alternating current into direct current or direct current into alternating current or alternating current of one frequency into alternating current of another frequency, comprising mechanical contact interrupters' each having a movable contact and a counter-contact and each being disposed respectively in one of the phases of the circuit of the converting device, a drive for actuating said movable contacts with a definite during the descending curve part of the current in the period immediately preceding the opening movement of said interrupter.

6. With a multiphase commutating device havpter opened is'shifted in accordance with the? current flow passing said interrupter ing movable break contacts for converting alternating current into direct current or direct current into alternating current or alternating current of one frequency into alte current of another frequency, in oom-binat a drive for actuating said contacts at the frequency of the current to be interrupted, an inductor in each phase connected in series with the contact of said phase, an arrangement for biasing said inductor so as to desultorily increase its inductance during the commutation period, a quick acting relay allotted to each phase and connected with said phase so as to be energized in correspondence with the voltage produced in said inductor by the commutation current and proportional to the speed with which the commutation current varies, and means operatively connected with said relay for biasing the movement of said contacts of the phase to be disconnected in such a manner that when the current passes the zero value, that minimum contact distance is attained but not essentially surpassed at which the flow of current in the reverse direction is prevented with certainty.

'7. A multiphase current converting device for converting alternating current into direct current or direct current into alternating current or alternating current of one frequency into alternating current of another frequency, comprising mechanical contact interrupters each having a movable contact and a counter-contact and each being disposed respectively in one of the phases of the circuit of the converting device, a drive for periodically actuating said movable contacts, an inductor connected in series with each of said interrupters, said inductors being designed to desultorily increase its inductance at the current values of the commutation period, a quick acting relay allotted to each phase and disposed to be energized in correspondence with the com-- mutation current, and a quick acting device controlled by said relays and designed to impart an additional movement to said counter-contacts, whereby the moment at which each interrupter opened is shifted in accordance with the current flow passing said interrupter during the descending curve part of the current in the period immediately preceding the opening movement of said interrupter.

8. A commutating device having movable break contacts for converting alternating current into direct current or direct current into alternating current or alternating current of one frequency into alternating current of another frequency, comprising quick acting means for periodically actuating said contacts, and an inductance in each phase connected in series with the contacts of said phase, said inductance having a magnetic core designed for attaining its state of saturation desultorily at an instantaneous current value lying below the average current value, said means being designed for initiating the opening of said contacts as soon as the instantaneous value of the current of the phase to be disconnected lies below the value necessary for saturating said core and for attaining the minimum break distance at which at the different loads the flow of current in the reverse direction is prevented with certainty at the latest at the moment at which the instantaneous value of the current again attains the value of saturation of said core.

9. A converting arrangement for transferring energy between an alternating current circuit and another circuit of different current characteristic,

a mechanical interrupter in each phase of said alternating current circuit, said interrupter having one of its contacts connected to said phase and the other connected with said other circuit, common driving means for operating said interrupters, said driving means being designed to run permanently during the operation period of the arrangement, an impedance in each of said phases series connected with the interrupter of said phase, an individual coupling disposed on each interrupter for periodically connecting said interrupter with said common driving means, said coupling having a magnetic device for effecting said connection, said magnetic device being electrically coupled with said impedance so as to be energized in correspondence with the current flowing through said interrupter, whereby each interrupter is actuated so as to open its phase circuit only after the current to be interrupted has decreased below a predetermined value.

10. In a converting arrangement for transferring energy between an alternating current circuit and another circuit of different current characteristics, an interrupting device having a movable contact and a counter-contact disposed between said circuits, means for actuating said movable contact with a given frequency, and quick acting means for imparting a movement to said counter-contact responsive to the energy transferred so as to shift the moment at which said interrupter opens in accordance with the energy amount passing said interrupter during the descending curve part of the current in the period immediately preceding the opening movement of said interrupter.

11. In a commutating arrangement for transferring energy between two circuits of different current characteristics, an interrupting device having a movable contact and a counter-contact disposed between said circuits, means for actuating said movable contact with the frequency of the current to be interrupted, an inductance series connected with said interrupter and designed to increase its inductance value at low current intensities within' the commutation period, and quick acting means for imparting a movement to said counter-contact so as to shift the moment at which said interrupter opens with respect to the voltage cycle of the current to be interrupted, said quick acting means being connected with said inductance so as to effect said shifting in correspondence with the voltage produced in said inductance by the commutation current and proportional to the speed with which the commutation current varies.

12. In a commutating arrangement for transferring energy between two circuits of different current characteristics, an interrupting device having a movable contact and a counter-contact disposed between said circuits, means for actuating said movable contact with a given frequency, an inductance series connected with aid interrupter and designed to increase its inductance value at low current intensities within the commutation period, and quick acting means for imparting a movement to said counter-contact responsive to the energy transferred so as to shift the moment at which said interrupter opens in accordance with the energy amount passing said interrupter during the descending curve part of the current in the period immedia" ly preceding the opening movement of said interrupter.

FRITZ KESSELRING. 

